Method and apparatus for encoding interplaced macroblock texture information

ABSTRACT

A method for padding interlaced texture information on a reference VOP to perform a motion estimation detects whether said each texture macroblock of the reference VOP is a boundary block or not. After the undefined texture pixels of the boundary block are extrapolated from the defined texture pixels thereof by using a horizontal repetitive padding, a transparent row padding and a transparent field padding sequentially, an undefined adjacent block is expanded based on the extrapolated boundary block.

More than one reissue application has been filed. The reissueapplication Ser. No. 12/131,723, filed Jun. 2, 2008, is a continuationof the present reissue application Ser. No. 12/131,712 filed Jun. 2,2008. The present reissue application Ser. No. 12/131,712 is acontinuation of reissue application Ser. No. 10/611,938 filed Jul. 3,2003, now abandoned, which is a reissue application of U.S. Pat. No.6,259,732 B1, which issued on Jul. 10, 2001 from U.S. application Ser.No. 09/088,375 and which claims priority under 35 U.S.C. 119 from KoreanPatent Application KR 98- 8637 filed Mar. 14, 1998.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for encodinginterlaced macroblock texture information; and, more particularly, to amethod and apparatus for padding interlaced texture information on areference VOP on a texture macroblock basis in order to perform a motionestimation while using the interlaced coding technique.

DESCRIPTION OF THE PRIOR ART

In digitally televised systems such as video-telephone, teleconferenceand high definition television systems, a large amount of digital datais needed to define each video frame signal since a video line signal inthe video frame signal comprises a sequence of digital data referred toas pixel values. Since, however, the available frequency bandwidth of aconventional transmission channel is limited, in order to transmit thelarge amount of digital data therethrough, it is necessary to compressor reduce the volume of data through the use of various data compressiontechniques, especially in the case of such low bit-rate video signalencoders as video-telephone and teleconference systems.

One of such techniques for encoding video signals for a low bit-rateencoding system is the so-called object-oriented analysis-synthesiscoding technique, wherein an input video image is divided into objects,and three sets of parameters for defining the motion, contour and pixeldata of each object are processed through different encoding channels.

One example of object-oriented coding scheme is the so-calledMPEG(Moving Picture Express Group) phase 4(MPEG-4), which is designed toprovide an audio-visual coding standard for allowing content-basedinteractivity, improved coding efficiency and/or universal accessibilityin such applications as low-bit rate communication, interactivemultimedia(e.g., games, interactive TV, etc.) and area surveillance(see,for instance, MPEG-4 Video Verification Model Version 7.0, InternationalOrganisation for Standardisation, ISO/IEC JTC1/SC29/WG11 MPEG97/N1642,Apr. 1997).

According to the MPEG-4, an input video image is divided into aplurality of video object planes(VOP's), which correspond to entities ina bitstream that a user can access and manipulate. A VOP can be referredto as an object and represented by a bounding rectangle whose width andheight may be the smallest multiples of 16 pixels(a macroblock size)surrounding each object so that the encoder may process the input videoimage on a VOP-by-VOP basis, i.e., an object-by-object basis.

A VOP disclosed in the MPEG-4 includes shape information and textureinformation for an object therein which are represented by a pluralityof macroblocks on the VOP, each of macroblocks having, e.g., 16×16pixels, wherein the shape information is represented in binary shapesignals and the texture information includes luminance and chrominancedata.

Since the texture information for two input video images sequentiallyreceived has temporal redundancies, it is desirable to reduce thetemporal redundancies therein by using a motion estimation andcompensation technique in order to efficiently encode the textureinformation.

In order to perform the motion estimation and compensation, a referenceVOP, e.g., a previous VOP, should be padded by a progressive imagepadding technique, i.e., a conventional repetitive padding technique. Inprinciple, the repetitive padding technique fills the transparent areaoutside the object of the VOP by repeating boundary pixels of theobject, wherein the boundary pixels are located on the contour of theobject. It is preferable to perform the repetitive padding techniquewith respect to the reconstructed shape information. If transparentpixels in a transparent area outside the object can be filled by therepetition of more than one boundary pixel, the average of the repeatedvalues is taken as a padded value. This progressive padding process isgenerally divided into 3 steps: a horizontal repetitive padding; avertical repetitive padding and an exterior padding(see, MPEG-4 VideoVerification Model Version 7.0)

While the progressive padding process as described above may be used toencode progressive texture information which has a larger spacialcorrelation between rows on a macroblock basis, the coding efficiencythereof may be low if the motion of an object within a VOP or a frame isconsiderably large. Therefore, prior to performing the motion estimationand compensation on a field-by-field basis for an interlaced textureinformation with the fast movement such as a sporting event, horseracing and car racing, an interlaced padding process may be preferableto the progressive padding process, wherein in the interlaced paddingprocess a macroblock is divided into two field blocks and padding iscarried out on a field block basis.

However, if all field blocks are padded without considering theircorrelation between fields, certain field blocks may not be properlypadded.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide a method andapparatus capable of padding the interlaced texture informationconsidering its correlation between fields.

In accordance with the invention, there is provided a method forencoding interlaced texture information on a texture macroblock basisthrough a motion estimation between a current VOP and its one or morereference VOP's, wherein each texture macroblock of the current and thereference VOP's has M×N defined or undefined texture pixels, M and Nbeing positive even integers, respectively, the method comprising thesteps of:

-   -   (a) detecting whether said each texture macroblock of each        reference VOP is a boundary block or not, wherein the boundary        block has at least one defined texture pixel and at least one        undefined texture pixel;    -   (b) dividing the boundary block into two field blocks, each        field block having M/2×N texture pixels;    -   (c) extrapolating the undefined texture pixels of each field        block based on the defined texture pixels thereof to generate an        extrapolated boundary block for said two field blocks; and    -   (d) if the boundary block has an undefined field block and a        defined field block, padding the undefined field block based on        the defined field block, wherein the undefined field block and        the defined field block represent one field block having the        undefined texture pixels only and the other field block having        at least one defined texture pixel, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodimentsgiven in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of an apparatus for encodinginterlaced texture information of an object in a video signal inaccordance with the present invention;

FIG. 2 presents a flow chart for illustrating the operation of thereference frame processing circuit shown in FIG. 1;

FIGS. 3A and 3B describe an exemplary boundary macroblock and a top anda bottom boundary field blocks for the boundary macroblock,respectively;

FIGS. 3C to 3E represent a padding procedure of the top and the bottomboundary field blocks sequentially in accordance with the presentinvention; and

FIG. 4 depicts a plurality of undefined adjacent blocks for an exemplaryVOP and the padding directions for each undefined adjacent block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a schematic block diagram of anapparatus for encoding texture information on a current VOP. The textureinformation partitioned into a plurality of texture macroblocks isapplied to a division circuit 102 on a texture macroblock basis, whereineach texture macroblock has M×N texture pixels, M and N being positiveeven integers typically ranging between 4 and 16.

The division circuit 102 divides each texture macroblock into a top anda bottom field blocks which may be referred to as interlaced textureinformation, wherein the top field block having M/2×N texture pixelscontains every odd row of each texture macroblock and the bottom fieldblock having the other M/2×N texture pixels contains every even row ofeach texture macroblock. The top and the bottom field blocks for eachtexture macroblock are sequentially provided as a current top and acurrent bottom field blocks, respectively, to a subtractor 104 and amotion estimator 116.

Reference, e.g., previous interlaced texture information, i.e.,interlaced texture information of a reference VOP, is read out from areference frame processing circuit 114 and provided to the motionestimator 116 and a motion compensator 118. The reference VOP is alsopartitioned into a plurality of search regions and each search region isdivided into a top and a bottom search regions, wherein the top searchregions having a predetermined number, e.g., P(M/2×N) of referencepixels contains every odd row of each search region of the bottom searchregion having the predetermined number of reference pixels containsevery even row of each search region, P being a positive integer,typically, 2.

The motion estimator 116 determines a motion vector for each current topor bottom field block on a field-by-field basis. First, the motionestimator 116 detects two reference field blocks, i.e., a reference topand a reference bottom field blocks for each current top or bottom fieldblock, wherein the two reference field blocks within the top and bottomsearch regions, respectively, are located at a same position as eachcurrent top or bottom field block. Since the top and the bottom searchregions have a plurality of candidate top and candidate bottom fieldblocks including the reference top and the reference bottom fieldblocks, respectively, each current top or bottom field can be displacedon a pixel-by-pixel basis within the top and the bottom search regionsto correspond with a candidate top and a candidate bottom field blocksfor each displacement, respectively; at all possible displacements,errors between each current top or bottom field block and all candidatetop and bottom field blocks therefore are calculated to be compared withone another; and selects, as an optimum candidate field block or a mostsimilar field block, a candidate top or bottom field block which yieldsa minimum error. Outputs from the motion estimator 116 are a motionvector and a field indication flag being provided to the motioncompensator 118 and a statistical coding circuit 108 by using, e.g., avariable length coding(VLC) discipline, wherein the motion vectordenotes a displacement between each current top or bottom field blockand the optimum candidate field block and the field indication flagrepresents whether the optimum candidate field block belongs, to the topsearch region or not.

The motion compensator 118 provides the optimum candidate field block asa predicted top or bottom field block for each current top or bottomfield block based on the motion vector and the field indication flag tothe subtractor 104 and an adder 112.

The subtractor 104 obtains an error field block by subtracting thepredicted top or bottom field block from each current top or bottomfield block on a corresponding pixel-by-pixel basis, to provide theerror field block to a texture encoding circuit 106.

In the texture encoding circuit 106, the error field block is subjectedto an orthogonal transform for removing spatial redundancy thereof andthen transform coefficients are quantized, to thereby provide thequantized transform coefficients to the statistical coding circuit 108and a texture reconstruction circuit 110. Since a conventionalorthogonal transform such as a discrete cosine transform(DCT) isperformed on a DCT block-by-DCT block basis, each DCT block havingtypically 8×8 texture pixels, the error field block having 8×16 errortexture pixels may be preferably divided into two DCT blocks in thetexture encoding circuit 106. If necessary, before performing the DCT,each error field block may be DCT-padded based on the shape informationor the reconstructed shape information of each VOP in order to reducehigher frequency components which may be generated in the DCTprocessing. For example, a predetermined value, e.g., ‘0’, may beassigned to the error texture pixels at the exterior of the contour ineach VOP.

The statistical coding circuit 108 performs a statistical encoding onthe quantized transform coefficients fed from the texture encodingcircuit 106 and the field indication flag and the motion vector, foreach current top or bottom field block, fed from the motion estimator116 by using, e.g., a conventional variable length coding technique, tothereby provide statistically encoded data to a transmitter (not shown)for the transmission thereof.

In the meantime, the texture reconstruction circuit 110 performs aninverse quantization and inverse transform on the quantized transformcoefficients to provide a reconstructed error field block, whichcorresponds to the error field block, to the adder 112. The adder 112combines the reconstructed error field block from the texturereconstruction circuit 110 and the predicted top or bottom field blockfrom the motion compensator 118 on a pixel-by-pixel basis, to therebyprovide a combined result as a reconstructed top or bottom field blockfor each current top or bottom field block to the reference frameprocessing circuit 114.

The reference frame processing circuit 114 sequentially pads thereconstructed top or bottom field block based on the shape informationor the reconstructed shape information for the current VOP, to therebystore the padded top and bottom field blocks as another referenceinterlaced texture information for a subsequent current VOP to themotion estimator 116 and the motion compensator 118.

Referring to FIG. 2, there is a flow chart for illustrating theoperation of the reference frame processing circuit 114 shown in FIG. 1.

At step S201, the reconstructed top or bottom field block issequentially received and, at step S203, exterior pixels in thereconstructed top or bottom field block are eliminated based on theshape information, wherein the exterior pixels are located at theoutside of the contour for the object. The reconstructed shapeinformation may be used on behalf of the shape information. While theexterior pixels are eliminated to be set as transparent pixels, i.e.,undefined texture pixels, the remaining interior pixels in thereconstructed top or bottom field block are provided as defined texturepixels on a field block-by-field block basis.

At step S204, each reconstructed block having a reconstructed top andits corresponding reconstructed bottom field blocks is determinedwhether or not being traversed by the contour of the object. In otherwords, each reconstructed block is determined as an interior block, aboundary block, or an exterior block, wherein the interior block hasonly the defined texture pixels, the exterior block has only theundefined texture pixels and the boundary block has both the definedtexture pixels and the undefined texture pixels. If the reconstructedblock is determined as an interior block, at step S210, no padding isperformed and the process goes to step S208.

If the reconstructed block is a boundary block BB as shown in FIG. 3A,at steps S221 to S224, the undefined texture pixels of the boundaryblock are extrapolated from the defined texture pixels thereof togenerate an extrapolated boundary block, wherein each of squares is atexture pixel, each shaded square being a defined texture pixel and eachwhite one being a undefined texture pixel.

First, at step S221, the boundary block is divided into a top and abottom boundary field blocks T and B as shown in FIG. 3B, wherein eachboundary field block has M2×N texture pixels, i.e., 8×16 texture pixelsso that the top and the bottom field blocks T and B have M/2, i.e., 8rows T1 to T8 and B1 to B8, respectively.

At step S222, the undefined texture pixels are padded on a row-by-rowbasis by using a horizontal repetitive padding technique as shown inFIG. 3C to generate a padded row for each of rows B1, B2 and B4 to B8.In other words, the undefined texture pixels are filled by repeatingboundary pixels toward the arrows as shown in FIG. 3C, wherein eachboundary pixel among the defined texture pixels is located on thecontour, i.e., the border, of the object. If there exist undefinedtexture pixels which may be padded by the repetition of more than oneboundary pixel, the average value of the repeated values is used.

If there exist one or more transparent rows, having the undefinedtexture pixels only, on each top or bottom field block, at step S223,each transparent row is padded by using one or more nearest defined orpadded rows among the corresponding top or bottom field block, whereinthe defined row has all the defined texture pixels therein. For example,as shown in FIG. 3D, each undefined texture pixel of the transparent rowB3 shown in the bottom field block is padded with an average of twodefined or padded texture pixels based on a nearest upward and a nearestdownward padded rows, i.e., the 2nd and the 4th padded rows B2 and B4 inthe bottom field block B. If the transparent row is located at thehighest or the lowest row, i.e., corresponds to the 1st row 1 or the 8throw, each texture pixel is padded with a defined or padded texture pixelof the nearest padded or defined row.

If there exists one transparent boundary field block in the boundaryblock as shown in FIG. 3B, at step S224, the transparent boundary fieldblock is padded based on the other boundary field block of the boundaryblock, wherein the transparent boundary field block, i.e., an undefinedfield block has no defined texture pixel therein. In other words, if atop field block is transparent, all the undefined texture pixels thereofmay be padded with a constant value P as shown in FIG. 3E, e.g., a meanvalue of the defined texture pixels within the bottom field block. Themean value of both the defined and the padded pixels within the bottomfield block can also be used to fill the transparent field block. Ifnecessary, a middle value 2_(L−1) of all the possible values for anytexture pixel may be used based on the channel characteristics, whereinL is the number of bits assigned for each pixel. For example, if L isequal to 8, there are 256 texture pixels 0 to 255 and the middle valueis determined to be 128.

After all the interior and boundary blocks are padded as describedabove, in order to cope with a VOP of fast motion, the padding must befurther extended to undefined adjacent blocks, i.e., exterior blockswhich are adjacent to one or more interior or boundary blocks. Theadjacent blocks can stretch outside the VOP, if necessary. At step S208,the undefined texture pixels in the undefined adjacent block are paddedbased on one of the extrapolated boundary blocks and the interior blocksto generate an extrapolated adjacent block for the undefined adjacentblock, wherein each extrapolated boundary block has a part of thecontour A of an object and each undefined adjacent block is shown as ashaded region as shown in FIG. 4. If more than one extrapolated boundaryblocks surround the undefined adjacent block, one of the left, theupper, the right and the below extrapolated boundary blocks of theundefined adjacent block is selected in this priority and, then, avertical or a horizontal border of the selected extrapolated boundaryblock is repeated rightwards, downwards, leftwards or upwards, whereinthe vertical or the horizontal border adjoins the undefined adjacentblock. As shown in FIG. 4, the undefined adjacent blocks JB4, JB10,JB15, JB21 and JB28 select their respective left extrapolated boundaryblocks a2, a5, a9, a13 and a14; the undefined adjacent blocks JB20, JB27and JB22 select their respective upper extrapolated boundary blocks a10,a14 and a13; the undefined adjacent blocks JB1, JB9, JB14 and JB19select their respective right extrapolated boundary blocks a1, a3, a6and a10; and the undefined adjacent blocks JB2 and JB3 select theirrespective below extrapolated boundary blocks a1 and a2. A rightmostvertical border of the extrapolated boundary block a2 is expandedrightward to fill the undefined adjacent block JB4, a lowermosthorizontal border of the extrapolated boundary block a10 is expandeddownward to fill the undefined adjacent block JB20 and so on. Also,undefined diagonal blocks such as M1, M2, MS and M7 to M11 may be paddedwith a constant value, e.g., ‘128’ to be the extrapolated adjacent blockfor the undefined diagonal block, wherein each undefined diagonal blockis diagonally adjacent to the extrapolated boundary block and has allundefined texture pixels.

As described above, at step S211, the extrapolated boundary and theextrapolated adjacent blocks as well as the interior blocks are stored.

While the present invention has been described with respect to theparticular embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A method for encoding interlaced texture information on a texturemacroblock basis through a motion estimation between a current VOP andits one or more reference VOP's, wherein each texture macroblock of thecurrent and the reference VOP's has M×N defined or undefined texturepixels, M and N being positive even integers, respectively, the methodcomprising the steps of: (a) detecting whether said each texturemacroblock of each reference VOP is a boundary block or not, wherein theboundary block has at least one defined texture pixel and at least oneundefined texture pixel; (b) dividing the boundary block into two fieldblocks, each field block having M/2×N texture pixels; (c) extrapolatingthe undefined texture pixels of each field block based on the definedtexture pixels thereof to generate an extrapolated boundary block forsaid two field blocks; (d) if the boundary block has an undefined fieldblock and a defined field block, padding the undefined field block basedon the defined field block, wherein the undefined field block and thedefined field block represent one field block having the undefinedtexture pixels only and the other field block having at least onedefined texture pixel, respectively; and (f) expanding an undefinedadjacent block based on the extrapolated boundary block, wherein theundefined adjacent block is adjacent to the extrapolated boundary blockand has only undefined texture pixels, wherein the step (c) furtherincludes the step of (c1) field-padding said at least one undefinedtexture pixel in a field block from said at least one defined texturepixel therein, to thereby generate a padded field block for the fieldblock, wherein the step (c1) has the steps of: (c11) row-padding said atleast one undefined texture pixel on a row-by-row basis to generate apadded row; and (c12) padding, if there exists a transparent row, thetransparent row from at least one nearest padded row, wherein thetransparent row represents a row having the undefined texture pixelsonly.
 2. The method as recited in claim 1, wherein said step (f)includes the steps of: (f1) selecting, if said undefined adjacent blockis surrounded by a plurality of extrapolated boundary blocks, one of theleft, the upper, the right and the below extrapolated boundary blocks ofsaid undefined adjacent block in this priority; and (f2) replicating avertical or a horizontal border of the selected extrapolated boundaryblock rightwards, downwards, leftwards or upwards, to thereby expand theundefined adjacent block, wherein the vertical or the horizontal borderadjoins said undefined adjacent block.
 3. The method as recited in claim1, wherein all the undefined texture pixels of said undefined fieldblock are padded with a constant value.
 4. The method as recited inclaim 3, wherein all the undefined texture pixels of said undefinedfield block are padded with a mean value of both the defined texturepixels and padded texture pixels within the padded field block for theother field block, wherein the padded texture pixels are field-paddedthrough the step (c1).
 5. The method as recited in claim 3, wherein allthe undefined texture pixels of said undefined field block are paddedwith a mean value of the defined texture pixels within the padded fieldblock for the other field block.
 6. The method as recited in claim 3,wherein the constant value is 2^(L−1), wherein L is the number of bitsassigned for each pixel.
 7. The method as recited in claim 6, wherein Lis
 8. 8. An apparatus for encoding interlaced texture information on atexture macroblock basis through a motion estimation between a currentVOP and its one or more reference VOP's, wherein each texture macroblockof the current and reference VOP's has M×N texture pixels, M and N beingpositive even integers, respectively, the apparatus comprising: aboundary block detector for detecting whether said each texturemacroblock of each reference VOP is a boundary block or not, wherein theboundary block has at least one defined texture pixel and at least oneundefined texture pixel; a field divider for dividing the boundary blockinto two field blocks, each field block having M/2×N texture pixels; atexture pixel padding circuit for extrapolating the undefined texturepixels of each field block based on the defined texture pixels thereofto generate an extrapolated boundary block for said two field blocks; atransparent field padding circuit for padding an undefined field blockof the boundary block based on the other field block thereof, whereinthe undefined field block represents a field block having the undefinedtexture pixels only; an adjacent block padding circuit for expanding anundefined adjacent block based on the extrapolated boundary block,wherein the undefined adjacent block is adjacent to the extrapolatedboundary block and has the undefined texture pixels only; and afield-padding circuit for field-padding the undefined texture pixels ina field block from the defined texture pixels therein, to therebygenerate a padded field block for the field block, wherein thefield-padding circuit includes: a horizontal padding circuit for paddingthe undefined texture pixels on a row-by-row basis to generate a paddedrow; and a transparent row padding circuit for padding the transparentrow from at least one nearest padded row, wherein the transparent rowrepresents a row having the defined texture pixels only.
 9. Theapparatus as recited in claim 8, wherein said adjacent block paddingcircuit includes: a selector for selecting one of the left, the upper,the right and the below extrapolated boundary blocks of said undefinedadjacent block in this priority; and means for replicating a vertical ora horizontal border of the selected extrapolated boundary blockrightwards, downwards, leftwards or upwards, to thereby expand theundefined adjacent block, wherein the vertical or the horizontal borderadjoins said undefined adjacent block.
 10. The apparatus as recited inclaim 8, wherein all the undefined texture pixels of said undefinedfield block are padded with a constant value.
 11. The apparatus asrecited in claim 10, wherein all the undefined texture pixels of saidundefined field block are padded with a mean value of both the definedtexture pixels and padded texture pixels within the padded field blockfor the other field block, wherein the padded texture pixels arefield-padded through the field-padding circuit.
 12. The apparatus asrecited in claim 10, wherein all the undefined texture pixels of saidundefined field block are padded with a mean value of the definedtexture pixels within the padded field block for the other field block.13. The apparatus as recited in claim 10, wherein the constant value is2^(L−1), L being the number of bits assigned for each pixel.
 14. Theapparatus as recited in claim 13, wherein L is
 8. 15. A method forencoding interlaced texture information on a texture macroblock basisusing a field prediction between a current VOP and its one or morereference VOP's, wherein the texture macroblock of the current VOP hasM×N defined or undefined texture pixels, M and N being positiveintegers, respectively, the method comprising: providing top field blockor bottom field block of the texture macroblock of the current VOP;determining a motion vector and a predicted top or bottom field blockfor each current top or bottom field block on a field-by-field basis,wherein the motion vector denotes a displacement between each currenttop or bottom field block and the predicted top or bottom field block ofthe reference VOP; obtaining an error field block by subtracting thepredicted top or bottom field block from each current top or bottomfield block on a corresponding pixel-by-pixel basis;discrete-cosine-transforming the error field block on a DCT block-by-DCTblock basis; quantizing the DCT coefficients; and performing astatistical encoding on the quantized DCT coefficients and motionvector, for each top or bottom field block, wherein the reference VOP isobtained by padding the previous reconstructed texture information basedon shape information, wherein when the previous reconstructed textureinformation is a boundary macroblock of interlaced VOP, (i) theundefined texture pixel in a row of the macroblock of interlaced VOP ispadded based on one or more of the defined texture pixels in said row,(ii) the undefined texture pixels in a row having only the undefinedtexture pixels are padded based on one or more of the defined texturepixels in another one or more rows having at least one defined texturepixel in same field block, and (iii) the field block has only theundefined texture pixels is padded with a constant value.
 16. The methodof claim 15, wherein the constant value is 2 ^(L−1) , wherein L is anumber of bits assigned for each pixel.
 17. The method of claim 15,wherein the constant value is
 128. 18. A method for encoding interlacedtexture information on a texture macroblock basis using a fieldprediction between a current VOP and its one or more reference VOP's,wherein the texture macroblock of the current VOP has M×N defined orundefined texture pixels, M and N being positive integers, respectively,the method comprising: providing top field block or bottom field blockof the texture macroblock of the current VOP; determining a motionvector and a predicted top or bottom field block for each current top orbottom field block on a field-by-field basis, wherein the motion vectordenotes a displacement between each current top or bottom field blockand the predicted top or bottom field block of the reference VOP;obtaining an error field block by subtracting the predicted top orbottom field block from each current top or bottom field block on acorresponding pixel-by-pixel basis; discrete-cosine-transforming theerror field block on a DCT block-by-DCT block basis; quantizing the DCTcoefficients; performing a statistical encoding on the quantized DCTcoefficients and motion vector, for each top or bottom field block;performing an inverse quantization and inverse transform on thequantized DCT coefficients to obtain a reconstructed error field block;combining the reconstructed error field block and the predicted top orbottom field block on a pixel-by-pixel basis; and padding areconstructed top or bottom field block based on shape information forthe current VOP, to thereby store the padded top or bottom field blocksas reference interlaced texture information, wherein the step of paddinga reconstructed top or bottom field block further includes the substepsof: padding the undefined texture pixel of the reconstructed boundarytop or bottom field block based on one or more the defined texturepixels in same field block, if the boundary top or bottom field blockhas only undefined texture pixels, padding the undefined texture pixelswith middle value 2 ^(L−1) of all the possible values for any texturepixel, expanding an undefined adjacent macroblock based on the paddedboundary macroblock, wherein the undefined adjacent macroblock isadjacent to the padded boundary macroblock and has only undefinedtexture pixels.
 19. The method of claim 18, wherein the substep ofpadding the undefined texture pixel of the reconstructed boundary top orbottom field block includes the steps of; row-padding at least oneundefined texture pixel on a row-by-row basis to generate a padded row,and padding, if there exist one or more transparent rows, thetransparent row based on at least one nearest padded row, wherein thetransparent row has only the undefined textures.
 20. The method of claim18, wherein the substep of expanding an undefined adjacent macroblockbased on the padded boundary macroblock includes the steps of;selecting, if said undefined adjacent block is surrounded by a pluralityof padded boundary macroblocks, one of the left, the upper, the rightand the below extrapolated boundary macroblocks of said undefinedadjacent macroblock in this priority, and replicating a vertical borderor a horizontal border of the selected padded boundary macroblockrightwards, downwards, leftwards or upwards.
 21. The method of claim 18,wherein middle value 2 ^(L−1) of all the possible values for any texturepixel is 128.